Rectangular shadow-mask-type color picture tube with barrel-shaped mask frame

ABSTRACT

A RECTANGULAR SHADOW-MASK TYPE COLOR PICTURE TUBE HAVING A SHADOW MASK COMPRISING AN APERTURED MASKING PORTION OF SPHERICAL CONTOUR AND HAVING A RECTANGULAR PERIPHERAL SKIRT PORTION ATTACHED TO ONE FLANGE OF A BARREL-SHAPED RECTANGULAR FRAME OF UNIFORM L-SHAPED CROSS SECTION, THE OTHER FLANGE OF WHICH EXTENDS INWARDLY TO SERVE AS AN ELECTRON SHIELD FOR THE SKIRT AND ONE FLANGE DURING OVERSCAN OF THE BEAM AT MAXIMUM DEFLECTION ANGLES. THE DIFFERENCE IN CURVATURE OF THE LONG AND SHORT SIDES OF THE BARREL-SHAPED FRAME IS SUCH THAT THE PORTIONS OF THE FRAME TO WHICH THE MOUNTING SPRINGS ARE ATTACHED LIE SUBSTANTIALLY IN A COMMON PLANE PERPENDICULAR TO THE CENTRAL TUBE AXIS, THUS PERMITTING THE USE OF IDENTICAL SPRINGS.

United States Patent Frank M. Sohn Lancaster. Pa. 783,186

Dec. 12, 1968 June 28, 1971 RCA Corporation lnventor Appl. Nov Filed Patented Assignee RECTANGULAR SHADOW-MASK-TYPE COLOR PICTURE TUBE WITH BARREL SHAPED MASK FRAME 7/1959 Fiore 313/85X 3,330,980 7/1967 Shrader 313/85 3,333,134 7/1967 Demmy 313/85 3.351.996 11/1967 Fiorc 313/85 Primary ExaminerRoy Lake Assistant Examiner--V. Lafranchi Attorney-Glenn H. Bruestle ABSTRACT: A rectangular shadow-mask-type color picture tube havinga shadow mask comprising an apertured masking portion of spherical contour and having a rectangular peripheral skirt portion attached to one flange of a barrelshaped rectangular frame of uniform L-shaped cross section, the other flange of which extends inwardly to serve as an electron shield for the skirt and one flange during overscan of the beam at maximum deflection angles. The difierence in curvature of the long and short sides of the barrel-shaped frame is such that the portions of the frame to which the mounting springs are attached lie substantially in a common plane perpendicular to the central tube axis, thus permitting the use of identical springs.

PATENTEDJUNZBISH 3,588,568

SHEET 2 OF 2 INVENTOR RECTANGULAR SHADOW-MASK-TYPE COLOR PICTURE TUBE WITH BARREL SHAPED MASK FRAME BACKGROUND OF THE INVENTION The present invention relates to rectangular shadow mask type color picture tubes, and particularly to an improved shadow mask frame for such a tube. a

In some rectangular shadow mask color picture tubes presently being manufactured, a spherically curved apertured masking member has a rectangular peripheral skirt attached to an axially extending flange of a rectangular frame of uniform L-shaped cross section, the other flange of which is spherically curved and extends inwardly to limit the impingement of the electron beam on the skirt and axial flange at max imum deflection angles, as disclosed in Demmy US. Pat. No. 3,333,134, granted July 25, I967. Particularly in wide-angle picture tubes, e.g. 90, the center of deflection of the electron beam or beams is much closer to the mask than is the center of curvature thereof. In a 90 rectangular tube, the maximum deflection angles are about 63 at the midpoints of the long sides, 79 at the midpoints of the short sides, and 90 at the four corners (diagonals). As a result of these different maximum deflection angles and the spherical curvature of the inwardly extending flange of the frame, the degree of shielding of the beam from the mask is nonuniform. This nonuniformity is greatest along the long sides of the frame, where the variation in maximum deflection angle is greatest (from 63 to 90).

Another disadvantage of the spherical contour of the conventional mask frame in a rectangular tube having four mask mounting studs and springs located near the midpoints of the four sides, is the fact that the portions of the frame to which the springs are attached lie in two different planes, one for each pair of opposite sides, spaced substantially from each other. This prevents the use of identical springs for all four support positions.

SUMMARY OF THE INVENTION An object of the present invention is to provide a rectangular shadow mask color picture tube having a novel mask frame.

A rectangular shadow mask color picture tube is provided with a mask electrode including a rectangular apertured mask ing member of spherical contour with a peripheral skirt at tached to a barrel-shaped rectangular frame of L-shaped cross section including an inwardly extending shield flange of uniform width. By the term barrel-shaped, it is meant that the shape of the rectangular frame is similar to the shape of the outline of a rectangular section of the round bulging side of a barrel, wherein the radius of curvature of the barrel staves is substantially greater than the maximum radius of curvature of the barrel hoops. The long sides of the inward flange of the frame have a surface curvature substantially smaller than the surface curvature of the long sides of the spherical masking member. The surface curvature of the short sides of the inward flange is greater than that of the long sides thereof, and preferably substantially the same as that of the short sides of the masking member. The difference in curvature between the long and short sides of the flange is such that the midpoints of the four sides lie substantially in a common plane perpendicular to the central tube axis, thus permitting the use of identical mounting springs. The term "surface curvature" is intended to mean curvature transverse to the plane of the frame as distinguished from the curvature of the outer edges of the masking member and frame in a radial direction.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side view of a rectangular shadow mask type color picture tube in which the present invention is embodied;

FIG. 2 is a transverse section view taken along line 2-2 of FIG. I;

FIG. 4 is a section view taken along line 4-4 of FIG. 3;

FIG. 3 is an enlarged section view taken on line 3-3 of FIG. I

FIGS. 5 and 6 are side views of the mask electrode of FIG. 2 taken in the directions of the arrows D and E, respectively; and

FIGS. 7, 8 and 9 are inverted section views taken on lines 7-7, 8-8 and 9-9, respectively, of FIG. 2

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. I shows the side of a rectangular color picture tube of the shadow mask type comprising a glass envelope 1 including a panel or cap 3 comprising a faceplate 4, a funnel 5 and a neck 7. An electron gun 9 within the neck 7 is adapted to project at least one, and preferably three, electron beams through a magnetic deflection yoke II which scans the beam in a rectangular raster over a mosaic color phosphor screen (not shown) on the inner surface of the faceplate 4. To produce color selection, a multiapertured shadow mask electrode 13 is mounted adjacent to the faceplate 4 in the path of the beams. FIG. 1 shows in dashed lines the average maximum vertical deflection angle of about 63 for the three beams in a rectangular tube.

As shown in FIG. 2, the mask electrode 13 and the skirt portion 14 of the cap 3 have similar generally rectangular shapes with rounded comers and major and minor axes 8-H and C-C, respectively. The mask electrode 13 comprises a rectangular curved sheet metal masking member 15 formed with a multiplicity of beam apertures 17, preferably arranged in a hexagonal array, and having a peripheral axially extending skirt 19 attached to a rectangular mounting and reinforcing frame 21. The frame 21 is a continuous metal strip of L-shaped cross section with curved sides as shown in FIGS. 3 to 6. The mask skin 19 telescopically engages and is welded to an axially extending flange 23 of the frame 21. The other flange 25 of the L-shaped frame is uniform in width and extends inwardly from flange 23 toward the central axis A-A of the tube to serve as an electron shield for preventing appreciable impingement of the beams on the mask skirt I9 and flange 23 during overscan of the beams at maximum deflection angles during operation of the tube (see FIGS. 79).

FIGS. 2-4 show the mask frame 21 detachably mounted in the envelope cap 14 by means of four studs 27, attached to the cap at points at or near the midpoints of the four sides of the cap, and four leaf springs 29 each having a triangular hole 31 near one end engaging one of the studs 27 and having its other end 33 welded to a temperaturecompensating bimetallic plate 34 which is welded to the frame 21, as disclosed in Shrader US. Pat. No. 3,330,980, granted July 11, I967. The plates 34 may be considered part of the frame 21. Moreover, the leaf springs 29 could be welded directly to the frame 21 (omitting the plates 34).

As shown in FIGS. 1 and 5-9, the inner surface of the faceplate 4 is concave and the adjacent surface of the masking member 15 is convex. Preferably both surfaces are spherical, with different centers of curvature on the axis A-A to produce a given variation in spacing therebetween from the center to the edge, as taught in Epstein et al. US. Pat. No. 3,109,]!6, granted Oct. 29, I963.

Instead of making the rectangular frame 21 of spherical shape to correspond to the spherical shape of the masking member I5, as in Demmy US. Pat. No. 3,333,l34, the frame 21, or at least the inward flange 25 thereof, is formed with a barrel shape wherein the surface curvature of the long sides 35 thereof transverse to the frame 21 is substantially less than the corresponding surface curvature of the short sides 37, and also substantially less than the corresponding surface curvature of the spherical masking member 15, as shown in FIGS. 5 and 6. The surface curvature of the short sides 37 of the flange 25 may be substantially the same as that of the spherical masking member I5. FIGS. 7 to 9 show the clearance between the shielding flange 25 and the electron beam (1) at each corner, (2) at the midpoint of each long side 35 and (3) at the mid point of each short side 37 at the maximum deflection angles 90", 63, and 79, respectively. The location of the inner edge of flange 25 in each of FIGS. 7-9 is such that the electron beam during overscan will be subjected to substantially uniform interception by the flange at each of the three positions shown, and also at other positions along the long sides. This results in substantially uniform shielding of the skirt l9 and flange 23 from the beam. For comparison, FIG. 8 shows in dotted lines 21' the position that the frame 2i would have at the midpoint of the long side 35 if the frame were formed with the same curvature as the masking member 15, as in the Demmy patent.

The surface curvature of the short sides 37 of the inward flange 25 could also be made less than that of the spherical masking member [5, to improve the uniformity of shielding along the short sides also during overscan. However, the nonuniformity along the short sides 37 is small, because the beam is deflected at a larger angle 79 for a shorter distance, and can be tolerated. Moreover, the surface curvature of the short sides 37 of the flange 25 is preferably made greater than that of the long sides 35, to improve the relationship of the frame 21 to the four mounting studs 27. The envelope caps 3 are ob tained from the bulb manufacturer with the four studs 27 located in a common plane G43 perpendicular to the central axis A-A. Thus, it is desirable that the central portions of the sides of the frame 21 to which the mounting springs are attached also lie in the same or a parallel common plane, in order to permit the use of identical springs at the four locations. This result is obtained, simultaneous with uniform shielding of the beam along the long sides 35 of the flange 25, with the barrel-shaped flange 25. The two different surface curvatures of the long and short sides 35 and 37, respectively, can be chosen so that the distances F, in FlGS. 5 and 6, between the common plane of the four corners of the flange and the central portions of the four sides are equal, so that these portions lie in a common plane parallel to the plane (1-0 of the studs 27, as shown in FIGS. 8 and 9, and still obtain sub stantially uniform shielding of the beam along the long sides 35. On the other hand, the two surface curvatures may be chosen primarily to obtain optimum uniformity of shielding; and incidentally to-locate the central portions of the four sides of the flange 25 substantially in the desired common plane, and thereby permit the use of identical springs.

Preferably, the frame 21 is formed with uniform cross section throughout, that is, with both flanges 23 and 25 having constant width. In this case, the entire flange is barrel-shaped, as described above for the inward flange 25, and the skirt 19 has variable width along the long sides, uniform width along the short sides, and uniform overlap of flange 23, as shown in FIGS. 5 and 6.

As an example, a 17-inch 90 rectangular color tube has a screen diagonal of about 16 inches, at faceplate radius of curvature of about 24 inches, a mask radius of curvature of about 25 inches. The barrel-shaped rectangular frame 2i may have a stave radius of curvature along the long sides of about 44 inches and a hoop radius of curvature along the short sides of about 27 inches, with the centers of curvature of the equatorial stave and hoop radii of the barrel-shaped surface containing the long and short sides of the frame lying on the central axis A-A. The widths of the axial and inward flanges may be about 0.7 inch and 0.5 inch, respectively.

While the example shown and described involves the use of four studs 27 and four springs 29 located at or near the midpoints of the four sides of the rectangle, the invention can also be applied to a similar rectangular color tube having the mask mounted on the envelope cap by three springs attached to the mask frame near the midpoints of three sides, as shown in Torrcnce U.S. Pat. No. 3,343,024, granted Sept. 19, l967. in this patent, the mask is mounted by one spring 25 attached to,the mask frame 30 near the midpoint of one long side and engaging a stud 17 at that midpoint, and two springs 26 and 27 attached to the mask frame near the midpoints of the two short sides and engaging studs l6 and 18 located between the midpoints and the ends of the short sides.

lclaim:

l. A shadow mask color picture tube comprising:

an envelope including a rectangular faceplate having a concave internal surface,

a mosaic color phosphor screen disposed on said surface,

electron gun means for projecting at least one beam ofelectrons toward said screen,

a rectangular shadow mask electrode disposed between said screen and said gun means, said mask electrode comprising a rectangular frame and a rectangular masking member mounted across said frame,

said masking member comprising a multiapertured curved portion having a convex surface facing said concave surface and a peripheral skirt extending away from said screen,

said frame comprising an endless strip of uniform L-shaped cross section, one of the flanges of the L extending toward said screen and being attached to said skirt, the other flange of the L extending inwardly from said one flange to serve as an electron shield during ovcrscan of the beam at maximum deflection angles,

said frame being barrel shaped, with the surface curvature of the two long sides of said frame transverse to the frame being substantially smaller than the corresponding surface curvature of the long sides of said masking member and also substantially smaller than the corresponding surface curvature ofthe short sides of said frame.

2. A shadow mask color picture tube comprising:

an envelope including a rectangular faceplate having a concave internal surface disposed perpendicularly to a central tube axis,

a mosaic color phosphor screen disposed on said surface,

electron gun means for projecting at least one beam of electrons toward said screen from a point near said axis,

a rectangular shadow mask electrode disposed between said screen and said gun means, said mask electrode comprising a rectangular frame and a rectangular sheet metal masking member mounted across said frame,

said masking member comprising a multiapcrtured portion having a convex surface facing said concave surface and a peripheral skirt extending away from said screen and parallel to said axis,

said frame comprising an endless curved strip of metal of L shaped cross section, one of the flanges of the L extending toward said screen and parallel to said axis and being attached to said skirt, the other flange of the L having uniform width and extending inwardly from said one flange for limiting the impingement of said beam on said skirt and said one flange during overscan at maximum deflection angles in the operation of said tube,

at least said other flange of said frame being substantially barrel shaped, as compared to the shape of said masking member, wherein the surface curvature of the two long sides of the rectangle of said other flange transverse to said frame is substantially smaller than the corresponding surface curvature of the long sides of said masking member.

3. A color tube as in claim 2, wherein said convex surface of said masking member is spherical, and the surface curvature of the short sides of the rectangle of said other flange transverse to said frame is substantially equal to the corresponding surface curvature of the short sides ofsaid masking member.

4. A color tube as in claim 2, wherein said frame is mounted in said envelope by at least three leaf springs each attached at one end to said frame and at the other end to a stud on said envelope, wherein said studs are located in a common plane perpendicular to said tube axis, and the portions of said other flange near the points of attachments of said springs to said frame lie substantially in a common plane parallel to said stud plane, whereby identicaL springs can be used.

5. A color tube as in claim 41, wherein four studs and four springs are located near the midpoints of the four sides of the rectangle.

6. A shadow mask color picture tube comprising:

an envelope including a rectangular faceplate having a concave internal surface disposed perpendicularly to a central tube axis,

at least three studs on said envelope located in a common plane perpendicular to said tube axis,

a mosaic color phosphor screen disposed on said surface,

electron gun means for projecting at least one beam of elec trons toward said screen from a point near said axis,

a rectangular shadow mask electrode disposed between said screen and said gun means. said electrode comprising a rectangular frame and a rectangular sheet metal maslting member mounted across said frame, 7

said masking member comprising a multiapertured portion having a convex surface facing said concave screen surface and a peripheral skirt extending away from said screen.

said frame comprising an endless curved strip of metal of uniform cross section attached to said skirt,

at least three leaf springs engaging said studs and each attached to one side of said frame near the midpoint thereof.

said frame being substantially barrel shaped, wherein the surface curvature of the two long sides of the rectangle transverse to said frame is substantially smaller than the corresponding surface curvature of the short sides thereof. the difference in curvature being such that the points of attachment of said springs lie substantially in a common plane parallel to said stud plane, whereby identical springs can be used. 

